Method for producing cellulose fiber having improved biostability

ABSTRACT

A cellulose fiber having extended biostability and the method of its manufacture are described. While prior treatments of cellulose with biotoxic metal compounds have given improved resistance to decay, these treatments have not been entirely satisfactory where the fiber had to be refined before use. Refining energy was very high and fiber length loss was substantial. Treatment of cellulose fiber with didecyldimethylammonium chloride (DDAC) or bromide (DDAB), these materials in combination with low levels of copper, or low levels of copper alone, has given a product with very good biostability without a major increase in refining energy or loss of fiber length. The treated fiber is particularly advantageous as a reinforcing component for cement board products.

[0001] This application is a continuation of application Ser. No.09/.838,947, filed Apr. 19, 2001, and now

[0002] The present invention is directed to a cellulose fiber havingexcellent resistance to environmental degradation, and to its method ofpreparation.

BACKGROUND OF THE INVENTION

[0003] Fiber reinforced cement board products used as building materialshave been in service since the second decade of the 1900s. Portlandcement serves as a matrix or binder for wood particles or strands. Inturn, the particles significantly reduce density and contributestrength, particularly tensile strength, to the product. Earlierproducts were made using wood excelsior as a reinforcing material.Later, asbestos fiber was widely used as a reinforcing fiber. The fiberis intimately mixed into a Portland cement-water slurry so that it isevenly coated. This mixture is predominantly formed into flat panelswhere the cement is allowed to cure before use. Alternatively, threedimensional products such as corrugated panels, roof tiles, and pipescan be made. Panels can be made with varying densities. Low densityproducts find interior applications as sound absorbent products forwalls and ceilings. Higher density panels are used as flooring, siding,sheathing, and concrete forms. For many years asbestos reinforcedsimulated shingles were widely used as siding for home construction.This application largely disappeared after the health problemsassociated with asbestos were uncovered. Today, cement board reinforcedwith cellulose fiber has made a significant comeback as a home sidingproduct. In this application it simulates horizontal or vertical woodsiding. Although the product requires special saws, it can otherwise beconventionally handled and nailed. Cement board siding is accepted as anattractive durable, dimensionally stable, low maintenance productresistant to moisture, decay, and insects.

[0004] Unbleached kraft pulps are predominantly used as the fiber sourcefor cement board siding. Soroushian et al., in Inorganic-Bonded Wood andFiber Composite Materials, A. A. Moslemi ed., 3: 9-19 Forest ProductsSociety (1993) (hereafter IBWFCM), generally describe the process ofmanufacture and properties of the resulting products. Similarly,Soroushian et al., in IBWFCM., 5: 3-7 (1997), describe a process foraccelerated curing of the products by autoclaving in high pressuresteam. Detailed layouts of plants for fiber reinforced cement boardproduction are given by K. Buchmayer, IBWFCM 6: 99-140 (1998), and G.Agansky, IBFWCM 6: 141-146, (1998). Briefly a slurry of the cellulosefibers is formed. Separately a slurry of cement, silica, filler, andother additives is prepared. These are mixed and formed into sheets orpanels, usually on an endless wire screen, where they are thendewatered. The dewatered panels are trimmed, pressed, and stacked. Theyare then autoclaved to accelerate hydration of the cement and induce atleast sufficient strength so that the panels can be handled withoutbreakage. Post curing and finishing are usually additional manufacturingsteps before the panels are shipped.

[0005] Today, the Hatschek wet process is the most widely usedproduction method. An aqueous slurry of fiber and cement with about7-10% solids is formed into sheets on several rotating cylinders.Several thin layers are superposed until a panel of the desiredthickness is formed. This is dewatered and cured as described above (seeConcrete Technology and Design: Natural Fibre Reinforced Cement andConcrete, R. N. Swamy, ed., Vol. 5, pp 23-25, Blackie, London).Typically about 10-30% by weight of the composite material will berefined cellulose fibers with the balance being inorganic mineralcomponents.

[0006] The manufacturing environment for cement bonded panels is veryhighly alkaline. As was noted, unbleached kraft fiber is frequently usedas reinforcement. Two problems have been attributed to use of kraftfiber, one during manufacturing and one during use. The first is due toalkaline leaching of materials not removed from the fiber in the pulpingprocess. These materials are generally degraded lignin and carbohydrateresidues. When present in excessive amounts they interfere with thecuring process and can deleteriously affect strength of the finishedproduct. Under some use conditions the fiber is subject to biologicalattack also resulting in weakening the product.

[0007] The present inventors are aware that some previous considerationhas been given to control biological degradation of cellulosicreinforcement in cement board products. They would note that chromatedcopper arsenate (CCA) treated wood particles have been used. This usehas not been with any intention of making biologically durable productsbut as a way of disposing of scrap or out-of-service CCA treated woodwhich is not suitable for use as fuel (see Hsu IBFWCM 4: 3-5 (1995), andP. A. Cooper et al. IBFWCM 6: 340-348 (1998)). The authors concludedthat CCA treated red pine was useable when comminuted into particles andthat the product could be made so that leaching of the toxic materialswas minor. Goodell et al., in Forest Products Journal 47(11/12): 75-80(1997), explored subsoil decay resistance of three wood-cement compositematerials. They concluded that only wood particles in the surfaceregions would likely be subject to fungal attack. Japanese PatentApplication 4333611 describes a cross linked acrylic fiber which may bemade from monomers that include multivalent metal acrylates. When themultivalent metals in the fiber are copper or zinc the fibers haveantibacterial properties. There was no suggested use of the fiber as acement board reinforcement. Japanese Patent 11-181619 describes apolypropylene fiber useful in cement boards. The fiber is resistant toautoclaving at temperatures as high as 170°-180° C. The fiber is meltspun with a zinc containing nucleating agent, said to contributeantimicrobial properties. Japanese Patent 3132552 describes a cementboard fiber containing 3-40% wood fiber having high durability. Thefiber is impregnated or coated with a metal compound selected fromcopper, zinc, aluminum or lead chloride or sulfate. Japanese PatentApplication 288149/87 describes wood reinforced cement boards in which asalt of iron, copper, lead, zinc, or aluminum is added to the mixingwater. The salt is said to react with components leached from the woodchips and to prevent hardening retardation caused by the leachates. Nomention was made of improvement in resistance to biological degradation.

[0008] Canadian Patent 1,134,564 describes cellulose fibers which aretreated for fungal resistance with metal oxide acylates in which themetal is selected from aluminum, titanium, copper, zinc, antimony,chromium, iron, manganese, or zirconium. Alternatively, other organicand inorganic metal compounds of copper, mercury, chromium, tin, andzinc were said to be useful. The treated fibers are suggested for use asan asbestos substitute in cement products, brake linings, gaskets, etc.

[0009] A significant problem with cellulose fibers treated with heavymetal biocides is that they require a high energy input and are subjectto considerable degradation during the refining process required for themanufacture of cement board products. The present invention hasaddressed and presents a solution to this problem.

SUMMARY OF THE INVENTION

[0010] The invention is directed to a fibrous cellulose productresistant to biological degradation, and to the method of making theproduct. It has been unexpectedly discovered that cellulose fibertreated with a compound selected from didecyldimethylammonium chloride(DDAC) or bromide (DDAB), DDAC or DDAB combined with small amounts ofcopper, or very low levels of copper alone, offers excellent protectionagainst biological deterioration when used as reinforcement in cementboard products. The fiber does not require significantly increasedenergy input levels or have serious fiber length degradation duringrefining. The amount of the copper compound included is below that atwhich significant interference with refining occurs.

[0011] DDAC and DDAB are useful in the range of 0.1% -2%, based on thedry weight of fiber present with 0.5% -1.0% being the preferred usage.Copper, as Cu based on weight of dry fiber, may be used in the range ofabout 0.01% -0.25% either alone or in combination with DDAC or DDAB.This may be added as any water soluble copper salt. The copper becomespermanently fixed on/in the fiber after exposure to the highly alkalineconditions encountered after mixing with Portland cement.

[0012] While an unbleached kraft fiber is a preferred raw materialbecause of its strength and cost, other chemically pulped cellulosefibers are known to be equally suitable. These include bleached kraftpulps, and bleached and unbleached sulfite and semichemical pulps, suchas chemithermomechanical pulps. When used as a reinforcement for cementboard products there is little incentive to use the more expensivebleached pulps even though their technical performance is equivalent tothe unbleached fibers.

[0013] The term “cement board products” should be read with sufficientbreadth to include flat panels or strips, corrugated panels, andcellulose fiber reinforced cement pipe. These products include thoseused for siding, roofing and tile backer among many others.

[0014] It is an object of the invention to provide a cellulose fiberhaving improved biostability that may be refined without significantlyincreased energy input.

[0015] It is a further object to provide a biostable cellulose fiberthat may be refined without significant fiber length loss or finesgeneration.

[0016] It is another object to provide a biostable cellulose fiberparticularly suitable for the manufacture of cement board products.

[0017] These and many other objects will become readily apparent uponreading the following detailed description of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Samples for testing were prepared by obtaining unbleached mixedconifer kraft pulp sheets produced in an interior British Columbia mill.The sheets were essentially unrefined and had a basis weight of about900 g/m². Solutions of various biocides were made up so that the desiredultimate concentration of active material would be obtained by sprayingeach sample portion of pulp sheet with about 1 g of the biocidalsolution per gram of pulp. The treated sheets were then air dried to fixthe active ingredient. Subsequently the treated sheets were reslurriedin water having a pH ˜12 obtained from a cement board manufacturingfacility and refined to a Canadian Standard Freeness (CSF) level of 450mL. All refining was done in a pilot scale Model 202 Claflin refiner(available from Bolton-Emerson, Inc., Lawrence, Mass.). The treated andrefined pulp was dewatered by centrifuging to a consistency of about 30%and then pin fluffed to ensure uniformity.

[0019] Treatments included copper sulfate at concentrations of 0.1, 0.3,and 0.5% Cu w/w based on dry pulp; zinc sulfate at concentrations of0.1%, 0.3%, and 0.6% Zn; 0.2% propiconazole emulsion;didecyldimethylammonium chloride (DDAC) 0.2%, 0.5%; and 1.0%, and 1.0%DDAB. Treated fibers were also made using 1.0% DDAC with 0.05%, 0.10%,and 0.2% Cu added as copper sulfate. All concentrations are on aweight/weight basis.

EXAMPLE 1

[0020] Examination of Samples for Biodurability

[0021] Samples of 30 g of the treated pulps were reslurried in water andformed into sheets in an 8×8 inch (203×203 mm) sheet. The sheets werepressed to remove excess moisture then air dried. Each sheet was thencut in half and dipped for 30 seconds in a slurry of one part Portlandcement in three parts by weight water. The coated and impregnated sheetswere removed and drained, allowed to cure for two days wet, and then airdried. Each 4×8 inch (151×203 mm) cement treated sheet was then enclosedin a 20 mesh stainless steel screen and half buried in the ground at atest site at Hilo, Hi. Samples were then removed after three month, sixmonth, nine month, and twelve month periods for examination. Exposedsheets were assigned a subjective rating for deterioration based onvisual observation (3=sound and 0=complete deterioration). The exposedsheets were also examined microscopically to determine the presence offungal mycelium and cell wall deterioration. Results of these tests areseen in Tables 1, 2, 3, and 4. TABLE 1 Results of 3 Months IngroundTesting Above Below Sample Ground Ground Fungi Presence Treatment RatingRating Above Ground Below Ground None 3 1 Yes - high Yes - low CuSO₄ -0.1% Cu 3 3 Yes - vy. low Yes - vy. low CuSO₄ - 0.3% Cu 3 3 No NoCuSO₄ - 0.5% Cu 3 3 Yes - vy. low No ZnSO₄ - 0.1% Zn 3 1 Yes - low Yes -medium ZnSO₄ - 0.3% Zn 3 1 Yes - low Yes - low ZnSO₄ - 0.6% Zn 3 1 Yes -low Yes - medium Propiconazole - 3 1 Yes - low Yes - medium 0.2% DDAC -0.2% 3 2 Yes - high Yes - med. high DDAC - 0.5% 2 2 No No DDAC - 1.0% 32.5 No Yes - vy. low DDAB - 1.0% 3 3 No No DDAC - 1.0% + 3 2.2 — — 0.05%Cu DDAC - 1.0% + 3 3 — — 0.1% Cu DDAC - 1.0% + 3 2.5 — — 0.2% Cu

[0022] Rating of 3 indicates sound. Rating of 0 indicates completedeterioration. TABLE 2 Results of 6 Months Inground Testing Above BelowSample Ground Ground Fungi Presence Treatment Rating* Rating* AboveGround Below Ground None 2 0 Yes - low No CuSO₄ - 0.1% Cu 3 1.5 Yes -vy. low Yes - high CuSO₄ - 0.3% Cu 3 3 No No CuSO₄ - 0.5% Cu 3 3 NoYes - vy. low ZnSO₄ - 0.1% Zn 3 1 Yes - vy. low Yes - med. high ZnSO₄ -0.3% Zn 3 1.3 Yes - med. low Yes - med. low ZnSO₄ - 0.6% Zn 3 0.5 Yes -high Yes - med. high DDAC - 0.2% 2.8 0.5 — — DDAC - 0.5% 3 1 — — DDAC -1.0% 3 2 — — Propiconazole - 3 0.5 Yes - vy. low Yes - low 0.2% DDAB -1.0% 2 2.8 Yes - vy. low Yes - vy. low DDAC - 1.0% + 3 0 — — 0.05% CuDDAC - 1.0% + 3 1 — — 0.1% Cu DDAC - 1.0% + 3 1 — — 0.2% Cu

[0023] TABLE 3 Results of 9 Months Inground Testing Above Below SampleGround Ground Treatment Rating* Rating* None 1.5 0 CuSO₄ - 0.1% Cu 3 1.5CuSO₄ - 0.3% Cu 3 2.3 CuSO₄ - 0.5% Cu 3 2.5 ZnSO₄ - 0.1% Zn 2.3 0ZnSO₄ - 0.3% Zn 3 0.8 ZnSO₄ - 0.6% Zn 2 0 Propiconazole - 2.8 0.5 0.2%DDAB - 1.0% 3 1.3 DDAC - 0.2% 2.8 0 DDAC - 0.5% 2.5 0 DDAC - 1.0% 3.01.5 DDAC - 1.0% + 0.05% Cu 2.3 0 DDAC - 1.0% + 0.1% Cu 3 0 DDAC - 1.0% +0.2% Cu 3 0

[0024] Based on the test conditions employed, effective below groundprotection was given by copper at concentrations of 0.3% or greater;DDAB at 1% (lower concentrations not tested); and DDAC at 0.5% orgreater. Addition of copper to 1.0% DDAC did not increase below groundprotection at nine months. Zinc compounds or propiconazole at 0.2% didnot give effective decay protection at any concentration tested. TABLE 4Results of 12 Months Inground Testing Above Below Sample Ground GroundTreatment Rating* Rating* None 2.3 0 CuSO₄ - 0.1% Cu 2.3 0.5 CuSO₄ -0.3% Cu 2 1 CuSO₄ - 0.5% Cu 3 2.3 ZnSO₄ - 0.1% Zn 2 0 ZnSO₄ - 0.3% Zn —— ZnSO₄ - 0.6% Zn 1.5 0 Propiconazole - 0.2% 2.3 0 DDAB - 1.0% — —DDAC - 0.2% — — DDAC - 0.5% — — DDAC - 1.0% — — DDAC - 1.0% + 0.05% Cu2.8 0 DDAC - 1.0% + 0.1% Cu 3 0 DDAC - 1.0% + 0.2% Cu 3 0

[0025] Only copper was effective in reducing cellulose fungal decayafter the one year underground tests. It should be noted that burial insurface soil in a semitropical environment is a very severe acceleratedaging test. The only cement board product likely to experience such anenvironment would be pipe. However, the test should be indicative oflong term durability above ground. With the exception of samples treatedwith only copper, the DDAC and DDAB treated material performed as wellas any of the other treatments. This treated fiber offers significantadvantages in refining energy and fiber length retention as comparedwith copper, as will be seen in the following examples.

EXAMPLE 2

[0026] Claflin Refining Tests of Biocidally Treated Pulps

[0027] Refining tests were run in duplicate on pulp samples prepared asin the previous example to determine energy input to constant freenessand evaluate the resulting fiber for damage. Refining times wereadjusted to attempt to get a freeness of about 450 mL C.S.F. In additionto the samples evaluated earlier, samples of DDAC with 0.05%, 0.10%, and0.20% copper were tested. Results are given in Table 5. TABLE 5 Resultsof Claflin Refining Tests Length Weighted Length Refining CS FiberWeighted Sample Energy, Freeness, Length, Fines Treatment MJ/t mL mm<0.2 mm, % Untreated¹ 920 450 2.31 4.8 Zinc sulfate-0.1% Zn 960 450 2.315.0 Zinc sulfate-0.3% Zn 970 500 2.21 5.2 Zinc sulfate-0.6% Zn² 1015 4502.20 5.7 Propiconazole-0.2% 980 460 2.18 5.6 Copper sulfate-0.1% 1060480 2.14 6.0 Cu Copper sulfate-0.3% 1410 470 1.61 8.0 Cu CopperSulfate-0.5% 2100 480 1.59 8.8 Cu Untreated³ 1251 460 2.35 5.2 1% DDAC +0.05% 1340 474 2.23 5.8 Cu 1% DDAC + 0.10% 1480 450 2.12 5.8 Cu 1%DDAC + 0.20% 1960 465 1.98 6.7 Cu

[0028] While the two higher levels of copper gave good biologicalprotection, it is immediately evident that the energy needed to refinethem was significantly increased over the untreated material. Fiberdamage was significant for the two higher levels of copper usage. Thezinc and propiconazole samples refined well but their biologicalprotection was poor. The use of up to 0.10% copper alone or with DDACdid not result in any major increase in required refining energy and didnot cause unacceptable loss of fiber length.

EXAMPLE 3

[0029] Results of Bird Escher Wyss Refining Tests

[0030] Samples of the unbleached Canadian kraft pulp used in the earliertests were made using 0.2%. 0.5%, and 1.0% DDAC based on dry pulpweight. A comparison sample was also made using a copper-chromiumtreatment with 0.2% Cu and 0.35% Cr. based on dry pulp weight. Thislatter treatment is one used commercially for wood exposed to conditionscausing decay. The samples were refined for this trial in a Model R 1 LBird Escher Wyss pilot plant scale refiner (available from Bird EscherWyss, Mansfield, Mass.). Again the attempt was made to refine to aconstant freeness value. The copper-chromium treated sample wasinadvertently refined some-what more heavily than desired. Energyconsumption results are given in Table 6. TABLE 6 Results of Escher-WyssRefining Tests Length Weighted Length Refining CS Fiber Weighted SampleEnergy, Freeness, Length, Fines Treatment MJ/t mL mm <0.2 mm, %Untreated¹ 2640 475 2.42 4.5 Copper chromate - 5440 320 2.06 6.0 0.2% Cuand 0.35% Cr DDAC - 0.2% 2680 445 2.30 6.2 DDAC - 0.5% 2720 448 2.30 4.9DDAC - 1.0% 2740 500 2.31 5.2

[0031] As in the previous example, there was no serious increase inrefining energy of loss of fiber length during refining in the DDACtreated samples. The copper-chromium treated sample required aboutdouble the refining energy of the other treated material. While somepart of this is due to the lower freeness of this sample, this does notbegin to account for the great increase noted. It was also observed thatthere was considerable leaching of the chromium from this sample.

[0032] Further tests have shown that the refined DDAC or DDAC pluscopper treated fiber has no inhibiting effect on the cure of concreteproducts using the fiber as reinforcement. The treated fibers handlednormally in every respect and were fully equivalent in manufacturingperformance and product physical properties to untreated material.However, as noted in Tables 1-3, durability under environmentalconditions that might induce fiber decay was greatly improved for theDDAC treated fibers.

[0033] It will be apparent to those skilled in the art that manyvariations in the preparation and use of the products of the inventioncould be made that have not been described herein. It is the intentionof the inventors that these variations should be included within thescope of the invention if encompassed within the following claims.

1. A cellulose fiber product resistant to biological degradation whichcomprises cellulose fibers derived from wood, the fibers initially beingat least partially purified by a chemical pulping process, the productcontaining a biocidally effective amount of a compound selected from thegroup consisting of didecyldimethylammonium chloride,didecyldimethylammonium bromide, and mixtures thereof, the fiber productbeing resistant to fiber length degradation during refining.
 2. Thecellulose fiber product of claim 1 in which the fiber product alsocontains 0.01-0.25% by weight of dry fiber of a water soluble coppersalt.
 3. The cellulose fiber product of claim 1 in which thedidecyldimethylammonium chloride, didecyldimethylammonium bromide, ormixture thereof is present in the fiber product in an amount of 0.1-2.0%by weight of dry fiber.
 4. The cellulose fiber product of claims 1 or 2in which the biocidal compound is didecyldimethylammonium chloride. 5.The cellulose fiber product of claims 1 or 2 in which the biocidalcompound is didecyldimethylammonium bromide.
 6. The cellulose fiberproduct of claims 1 or 2 in which the cellulose fiber is selected fromthe group consisting of bleached and unbleached kraft pulps, bleachedand unbleached sulfite pulps, bleached and unbleached semichemicalpulps, and bleached and unbleached chemithermomechanical pulps.
 7. Thecellulose fiber product of claim 6 in which the cellulose fiber is anunbleached kraft fiber.
 8. A method for producing a cellulose fiberproduct resistant to biological degradation which comprises: providing acellulose fiber derived from wood that has been at least partiallypurified by a chemical pulping process; treating the fiber so that itcontains a biocidally effective amount of a biocidal compositionselected from the group consisting of didecyldimethylammonium chloride,didecyldimethylammonium bromide and mixtures thereof; and drying thetreated fiber.
 9. The method of claim 8 in which the fiber is alsotreated to contain 0.01-0.25% of a water soluble copper salt.
 10. Themethod of claim 8 in which the didecyldimethylammonium chloride,didecyldimethylammonium bromide, or mixture thereof is present in thefiber in an amount of 0.1-2.0% by weight of dry fiber.
 11. The method ofclaims 8 or 9 in which the biocidal composition isdidecyldimethylammonium chloride.
 12. The method of claims 8 or 9 inwhich the biocidal composition is didecyldimethylammonium bromide. 13.The method of claims 8 or 9 in which the cellulose fiber is anunbleached kraft fiber.
 14. A cellulose fiber product resistant tobiological degradation which comprises cellulose fibers derived fromwood, the fibers initially being at least partially purified by achemical pulping process and containing 0.01-0.25% by weight of dryfiber of a biocidally effective water soluble copper salt, the fiberproduct being resistant to fiber length degradation during refining. 15.The cellulose fiber product of claim 14 which further includes incombination with the copper salt a biocidally effective amount of acompound selected from the group consisting of didecyldimethylammoniumchloride, didecyldimethylammonium bromide, and mixtures thereof.
 16. Thecellulose fiber product of claim 15 in which the didecyldimethylammoniumchloride, didecyldimethylammonium bromide, or mixture thereof is presentin an amount of 0.1-2.0% by weight of dry fiber.
 17. The celluloseproduct of claims 14 or 15 in which the cellulose fiber is an unbleachedkraft fiber.
 18. A method for producing a cellulose fiber productresistant to biological degradation which comprises: providing a woodderived cellulose fiber that has been at least partially purified by achemical pulping process treating the fiber with a biocidally effectiveamount of a water soluble copper salt to obtain a copper content in thefiber in the range from 0.01-0.25% by weight of the fiber; and dryingthe fiber.
 19. The method of claim 18 which further includes incombination with the copper salt a biocidally effective amount of acompound selected from the group consisting of didecyldimethylammoniumchloride, didecyldimethylammonium bromide, and mixtures thereof.
 20. Themethod of claim 19 in which the didecyldimethylammonium chloride,didecyldimethylammonium bromide, or mixtures thereof is present in anamount of 0.1-2.0% by weight of the dry fiber.
 21. The method of claim16 in which the cellulose fiber is an unbleached kraft fiber.